1. Field of the Invention:
This invention relates to compact zoom lenses, and more particularly to compact zoom lenses of short total length (the distance from the front vertex to the image plane) suited to lens-shutter cameras, video cameras or the like.
2. Description of the Prior Art:
The recent trend of reducing the size of lens shutter cameras, video cameras, or the like demands for compact zoom lenses of short total length. Particularly in the field of small size cameras whose objective lenses are not interchangeable, too, it is desired to use zoom lenses. For this purpose, the total length of the zoom lens has to be reduced to the same level as the fixed focal length lens that has so far been used has.
Many zoom lenses whose range includes the standard image angle for the ordinary lens-shutter cameras (the total angle of field 2.omega.=47.degree. with a focal length of about 50mm for 35mm still cameras) have been proposed in, for example, Japanese Patent Publication No. SHO 49-29146. The zoom lens of this kind is constructed by two lens units of which the front is of negative power and rear is of positive power, and its focal length is varied by varying the separation between the two lens units. However, because its refractive power arrangement is negative-positive in this order from the front, the back focal distance is relatively long. This tends to make too long the total length of the lens when it applies to the lens-shutter camera, though it is suited to the single lens reflex camera.
Further in Japanese Laid-Open patent application No. SHO 56-128911 (corresponding to U.S. patent application Ser. No. 243,209 field Mar. 12, 1981 assigned to the assignee of this invention) and Japanese Laid-Open patent application No. SHO 57-201213 there have been proposed compact zoom lenses each comprising a front lens unit of positive power and a rear lens unit of negative power with the separation therebetween being varied to vary the focal length of the entire system. The use of such positive-negative power arrangement leads not only to relatively shorten the back focal distance but also to achieve a zoom lens of short total length.